Method of calcining alunite



H. F. CHAPPELL.

METHOD OF CALCINING ALUNITE.

APPLICATION FILED MAY 2a, 1918. RENEWED OCT. 29, 1921.

Patented Dec. 27, 1921.

' anve'nfo'l, $41,011 5; cam am %1 7 8 arrow e135 UNITED STATES PATENT OFFICE.

HOWARD FIELD CHAPPELL, OF NEW YORK, N. Y.

METHOD OF CALCININ G ALUNI'IE.

Application filed May 28, 1918, Serial No. 236,981. Renewed October 29, 1921.

To all whomc't may concern:

Be it known that I, HOWARD F. CHAPPELL, a citizen of the United States, residing at New York, in thecounty of New York, State of New York, have invented certain new and useful Improvements in Methods of Calcining Alunite; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention relates to an improved method of calcining alunite, or the like.

In U. S. Letters Patent No. 1,070,324, granted to me on August 12, 1913, I have described the process of obtaining aluminum oxid and potassium sulfate from natural deposits of alum stone, alum rock, or alunite, by calcining the alunite, or the like, until the aluminum content thereof is substantially converted into insoluble aluminum oxid and the potassium content thereof is converted into potassium sulfate.

According to the process described in said prior patent, combustion is effected in a separate combustion chamber, and the products of combustion together with further amounts of air, are brought into the furnace where the calcination is effected, under oxidizing conditions.

I have now found that completion of the combustion, before bringing the products of combustion into contact with the alunite, is not necessary, and, that important economies and advantages can be secured by subjecting the alunite to the direct heat of combustion, provided the alunite is first freed from the greater portion'of its fumes of oxids of sulfur. Accordingly, in the process of the present invention, I first subject the alunite to the action of the hot products of combustion until the greater portion of such fumes have been emitted, and I then subject it to further heating. to complete the calcination, by bringing it into the combustion zone of the furnace and subjecting it to direct heating therein.

The process of the present invention can, with advantage, be carried out in a contlnuous manner, by effecting the combustion 1n the combustion zone of the furnace through which the alunite, free from the greater por tion of the fumes, is caused to pass, and then passing the products of combustion through Specification of Letters Patent.

Patented Dec. 27, 1921.

Serial No. 511,447.

the fume emitting zone to effect the heating of the alunite and the removal of the greater portion of the fumes therefrom.

-The present invention is based primarily upon .the discovery that in calcining alunite in a rotary kiln, it is important that the zone of combustion of the fuel should be nearer to the discharge end of the kiln than the point at which substantially all of the oxid of sulfur fumes are removed from the calcined alunite. In other words, substantially complete combustion of the fuel should take place before the combustion gases come in contact with the said fumes. If this condition is not maintained during the calcinmg of the alunite, I have found that several diificulties are likely to arise.

In the first place. if the oxid of sulfur fumes which are evolved from the alunite during the calcining thereof are mixed in any considerable quantities with the fuel vapors or gases before practically complete oxidation or combustion of the latter, it is difficult if not impossible to maintain a suffic ently high temperature to thoroughly or suitably calcine the alunite, no matter how much fuel, or how much air may be introduced. Thus, if the oxid of sulfur fumes evolved from the alunite mix with the incompletely ignited fuel vapors or gases a portion of the fuel passes over the ore before it is burned or consumed. This condition may be remedied for a time, when employing oil as the fuel, by using an excess of air or by using a steam jet, but the remedy is effective for only a few minutes, and such expedients are objectionable because of the great loss in dust which results from their use.

The proper calcination of the alunite is a" matter of particular importance from a practical standpoint. If the alunite is not properly calcined, there is not only a loss of potassium compounds and alumina in the unroasted portion of the ore, but potash alum is formed Which attacks the pipes and all the apparatus used in the subsequent extraction and recovery of the potassium compounds. Furthermore, if the incompletely ignited fuel gases come in contact with the alunite before the complete evolution of the oxid of sulfur gases therefrom, the potassium compounds are reduced to sulfid, and the leaching liquors become alkaline, which has a very deleterious effect on the leaching operation. Furthermore, under such conditions of calcination, there is a much heavier loss of potassium comunds from volatilization, and the dust oss is greater.

The present invention involves the calcining of alunite, or the like, under such conditions that the'combustion is effected or completed in the presence of alunite from which the major part of the, fumes have been removed, and also under such conditions that the products of the, combustion of the fuel are completely oxidized or burned before mingling with the oxid of sulfur fumes evolved from the ore. In calcining alunite, or the like, in a rotary kiln, there is a zone, in the travel of the ore from the entrance or feed end of the kiln to its discharge end, beyond which substantially no gases or only relatively small amounts of gases are evolved from the ore. In accordance with my present invention, the operating conditions are so maintained that this zone is nearer the entrance or feed end of the kiln I than is the zone of combustion of the fuel. Thus the invention involves the maintenance of such conditions that the zone of combustion of the fuel is not substantially contaminated with the fumes evolved from the ore, while the alunite from which the major part of the fumes have been removed is passed directly into and through such combustion zone.

In the accompanying drawing, I have illustrated an apparatus particularly devised for the practice of the improved method of my present invention. This apparatus is generally of the rotary kiln type, but involves certain modifications which particularly adapt it for calcining alunite in accordance with the present invention.

The calcining apparatus illustrated in the accompanying drawing comprises a rotary kiln 5, of substantially the same general type as employed in calcming cement, lime, or the like. This kiln is inclined so that during its rotation the material fed into the upper end thereof gradually travels toward the lower end from which it is discharged into a suitable receptacle, conveyer, or the like. The alunite is fed into the front or upper end of the kiln 5 by means of a suitable feed hopper 6. This end of the kiln projects into a settling chamber 7 provided with an adjustable damper 8 and a stack 9, from which the fumes evolved during the calcining of the alunite may be withdrawn.

In accordance with my present invention, a movable fire-box is associated with the lower or discharge end of the kiln 5. The movable fire-box comprises a short cylinder 10 of substantially the same diameter as the kiln. The length of the cylinder 10 will,

of course, depend to some extent, upon the size of the apparatus in general, but in the case of an ordinary cement kiln 135 ft. long, I have found length of about 5 feet to be satisfactory. The cylinder 10 is mounted on a truck 11, and is thus adapted to be moved toward or away from the lower or discharge end of the kiln 5. The cylinder 10 is provided with a suitable fuel injector burner 12 of any suitable type. The other end of the cylinder is designed to abut directly against the discharge end of the kiln.

A cylindrical ring or shell 13 is secured to the lower end of the kiln 5 and is separated from the outer surface of the kiln by an air space. A current of air is adapted to be blown into this air space by means of the air pipe 14, and in this manner the lower or discharge end of the kiln is suitably cooled. A sealing ring 15 is resiliently and slidably mounted on the outside of the shell 13 by-means of springs 16 and bolts 17. An apron 18 is secured to the cylinder 10 of the movablefire-box and has an outer ring or flange 19 adapted to engage the ring 15 and form therewith a substantially air tight seal around the junction of the kiln and fire box when the latter is in its operative position. i

The sealing means between the kiln and the fire-box effectively prevents the entrance into the kiln of any air, other than that admitted with the fuel through the burner 12. When the entrance of air is thus prevented around the end of the kiln, it becomes necessary to cool the end of the kiln, and the current of air provided by the air pipe 14 and the air-cooling space between thekiln and the shell 13 proves very effectiye for this purpose. As the kiln expands, the fire-box is pushed backward, but due to the resilient mounting of the sealing ring 15, the air-tight seal between the kiln and the fire-box is maintained. A discharge chute 20 is preferably associated with the movable fire-box and the calcined alunite drops through the chute into any suitable receptacle or conveyer. The gas pressure within the kiln will be sufficient to prevent the entrance through this chute of air into the lower end of the kiln when the kiln is in operation.

If for the sake of brevity we call'the feed end of the kiln the front end, and the discharge end the back end, then, in accordance with my present invention, the fuel used for calcination must be practically completely burned in a zone which is behind the zone giving off oxid of sulfur gases in any considerable amount. Assuming that powdered coal is used as the fuel, and the kiln is being fed to its capacity with alunite ore, the maximum capacity of the kiln is obtained when the combustion zone is held at a definite point as near the back end of the kiln as possible, and the zone where the oxid of sulfur gases are substantiall entirely eliminated is held immediate y in front of the maximum combustion zone.

The relation between the combustion zone and the zone of fume evolution is affected by several factors. I have found that the following conditions are important for such a maintenance of the combustion and fume zones as is contemplated by my present invention. The ore fed into the kiln should beof a substantially uniform size, and the feed should be as nearly uniform as possible. The kiln should likewise be rotated at a substantially uniform speed, in order that the travel of the ore through the kiln may be substantially uniform. In using pulverized coal as a fuel, the coal should be of a substantially uniform fineness, and its com position should be substantially uniform. In particular, the amount of moisture associated with the pulverized coal should be as uniformly distributed as possible. Then too, the mixture of the pulverized coal with the air, for combustion, should be maintained substantially uniform. By giving careful attention to these preliminary precautions, and by excluding the entrance of an excessive or uncontrolled amount of false air into the discharge or lower end of the kiln, the position of the combustion zone can be so maintained that the fuel is not contaminated during combustion by fumes evolved from the alunite.

By means of the burner and movable fire-box illustrated in the accompanying drawing, I have been able to obtain almost complete combustion of powdered coal in a zone ranging from 10 to 25 feet from the discharge end of the kiln. When the operator observes dense fumes of sulfuric acid emitting from the calcined ore from the discharge end of the kiln, he immediately slows down the speed of the kiln. which also slows down the feed of the kiln. Frequently, in a few minutes the ore will stop giving off acid fumes and remain neutral in action without giving off fumes for hours at a time. If the kiln were not stopped or other means taken to remove the fumes from the combustion zone, complete combustion gases would quickly cease, the kiln would grow colder. under-calcined ore would be discharged, fumes would increase greatly, and if conditions were not corrected no ore could be properly or completely calcined.

the kiln, other than that admitted with the fuel through the burner 12,- should be prevented as far as possible, since it tends to shift the combustion zone. By using the type of burner and movable fire-box illustrated in the accompanying drawing and by keeping the combustion zone very close to the discharge end of the kiln, there is created a sudden expansion of gases at this point which goes a long way to overcome any excessive air leaks at. the fire-box or around the end of the kiln. Furthermore, by carefully regulating the damper 8, the leaking of false air into the fire-box end of the kiln can be materially I minimized. F urthermore, the construction of the substantially air-tight seal between the lower end of the kiln and the movable fire-box is such as to effectively prevent the entrance of much false air into this end of the kiln, although a small amount of air may even be admitted at this point without materially interfering with the desired relationship between the combustion zone and the fumeemitting zone. In this manner, and by observing the precautions hereinbefore mentioned, the conditions of operation are maintained substantially uniform, and the necessar relation between the combustion zone am the fume-emitting zone is satisfactorily maintained.

Among the advantages of the present invention may be mentioned an important economy in fuel, increased temperature in the calcining furnace, increased output, the avoidance of the necessity of any large ex- 100 cess of air or oxygen, more effective heating of the alunite undergoing calcination, and reduction in the wear and tear on the combustion chamber where this chamber is protected by the alunite undergoing calcination. 106

Having thus described my invention, what I claim is:

1. The method .of calcining alunite or the like, which comprises subjectingthe alunite to the direct heating action of the flame of a 110 combustible fuel and of the hot products of combustion thereof, and effecting a substantially complete combustion of the fuel before the gaseous products of combustion thereof come in contact with that ortion of the 115 alunite from which substantially all of the fumes are being evolved by the calcining operations; substantially as described.

2. The method of calcining alunite or the like, which comprises feeding the alunite 120 into one end of a rotary kiln, supplying a combustible fuel to the other end of said kiln, and effecting a substantially complete combustion of said fuel before the products of combustion thereof mingle with the fumes 125 evolved from the alunite; substantially as described.

3. The method of calcining alunite or the like, which comprises effecting combustion of a combustible fuel in the presence of alun- 130 its from which the greater part of the fumes have been emitted, and subjecting the alunite to the action of the hot gaseous products of combustion, and maintaining such a relation between the zone of combustion of the fuel and the zone atwhich substantially all of the fumes are emitted from the alunite that the fuel is substantially completely consumed before the products of combustion thereof mingle with the fumes emitted from the alunite; substantially as described.

4. The method of calcining alunite and the like, which comprises heating the alunite, after the greater portion of the fumes of oxids of sulfur have been emitted therefrom, by effecting combustion of a suitable fuel in the presence thereof.

5. The method of calcining alunite or the like, which comprises subjecting the alunite to the heating action of products of combustion, after substantially complete combustion thereof, until the greater portion of the fumes of oxids of sulfur have been emitted therefrom, and then to the direct heat of combustion to complete the calcination.

6. The method of calcining alunite or the like, which comprises effecting combustion of a suitable fuel in the presence of the alunite from which the greater portion of the fumes of oxids of sulfur have been emitted, and passing the products of combustion over uncalcined alunite to effect the emission of such fumes therefrom.

7. The methods of calcining alunite or the like, which comprises effecting combustion of a suitable fuel in a furnace chamber through which alunite, freed from the greater portion of its fumes of oxids of sulfur, is passing.

'8. The method of calcining alunite or the like in a continuous manner, which comprises passing the alunite continuously through a furnace zone heated by products of combustion, until the greater portion of the fumes of oxids of sulfur have been emitted therefrom, and then through a furnace zone in which active combustion is taking place. i

9. The method of calcining alunite or the like, which comprises feeding the alunite into one end of a rotary kiln, supplying a substantially uniform mixture of a combustible fuel and air to the other or combustion end of said kiln, excluding the entrance into the combustion end of said kiln of substantally any other air, and effecting a substantially complete combustion of said fuel before the products of combustion thereof mingle with the fumes emitted from the alunite; substantially as described.

10. The method of calcining alunite or the like, during which fumes of oxids of sulfur are emitted, which comprises feeding the alunite into one end of a rotary kiln; supplying a combustible fuel to the other or combustion end of said kiln, and maintaining the zone of combustion of said fuel nearer to the combustion end of said kiln than is the zone of said fume emission; substantially as described.

11. The method of calcining alunite or the like, which comprises feeding the alunite in a substantially uniform size and condition into one end of a rotary kiln, supplying a substantially uniform mixture of air and pulverized coal of a substantially uniform HOWARD FIELD CHAPPELL 

